Electrophorestic separation using a capillary or a microfluidics chip has been used widely as an analysis method capable of analyzing a small amount of a sample in a short time and in high precision. However, there is a problem of insufficient sensitivity caused by small amount of the sample which can be injected at the inside of the capillary.
To resolve this problem, there has been proposed a method for preliminary separating and concentrating (an on-line pre-concentration method) a sample by isotachophoresis (ITP) etc., and then for providing thus separated and concentrated sample to capillary electrophoresis (CZE) or capillary gel electrophoresis (CGE) (Patent Literature 1, Patent Literature 2 etc.).
ITP is based on principle that, by applying a voltage in a state that a sample including the analyte is sandwiched between an electrophoresis medium (a leading buffer: LB) including a leading ion having faster (larger) electrophoretic mobility than that of the analyte in the sample, and an electrophoresis medium including a trailing ion having slower (smaller) electrophoretic speed than that of the analyte in the sample (a trailing buffer: TB), the analyte is concentrated, while the analyte can be separated from other components in the sample.
On the other hand, there has been proposed a method for enhancing separation efficiency between the analyte and other components, by using a spacer ion having intermediate electrophoretic mobility between electrophoretic mobility of the analyte and electrophoretic mobility of other components to be separated, in ITP, and thus by distributing the analyte and components to be separated, before and after said spacer ion; and various spacer ions to be used (Patent Literature 3, Non-Patent Literature 1 etc.).